Semaglutide's Melting Point and What It Means for Real-World Use

Why doesn't semaglutide have a straightforward melting point?

The question comes up often, and it's a reasonable one. Most substances we think of as having a melting point are small, crystalline molecules with a tight lattice structure that collapses at a predictable temperature. Semaglutide is something entirely different: a 31-amino-acid peptide with a fatty-acid side chain attached, giving it the unusually long half-life that allows once-weekly dosing. Molecules like this don't melt, they denature.

Denaturation means the protein's three-dimensional shape unravels. The peptide bonds holding the chain together don't necessarily break, but the folded structure that makes the molecule biologically active does. Once that shape is gone, the molecule can no longer bind to GLP-1 receptors in the way it should. The liquid in your pen may look perfectly clear and colourless, denaturation is invisible to the naked eye.

This is precisely why the storage instructions in the Wegovy Patient Information Leaflet are so specific, and why following them matters more than it might seem. You can read about semaglutide's pharmacological profile in more depth on our semaglutide overview page.

At what temperatures does semaglutide become unstable?

The formally permitted storage ranges for Wegovy are set out in the SmPC and Patient Information Leaflet, the most reliable source is the Mounjaro and Wegovy SmPCs on the eMC, which are updated whenever Novo Nordisk revises the product documentation. As a general principle: refrigeration at 2–8°C is required for unopened pens. Once a pen is in use (or has been removed from the fridge), a room-temperature window applies, but the exact duration differs by product format, and the leaflet states it precisely. Do not rely on a general figure you find online.

What we know from peptide biochemistry is that temperatures above roughly 30–40°C begin to accelerate denaturation significantly, and anything approaching 50°C or beyond is likely to cause rapid loss of potency. Freezing is equally damaging: ice crystal formation disrupts the liquid formulation, and a frozen-then-thawed pen should not be used. That rules out car gloveboxes in summer, window sills, and the freezer compartment of a fridge-freezer with a faulty seal.

Our Wegovy treatment page explains the full picture of how semaglutide is dispensed and what to expect from your pen.

What should you do if your pen has been exposed to the wrong temperature?

This is the practical question most people are actually asking when they search for the melting point. The honest answer: if you're not sure, don't use it. A compromised pen won't necessarily look different. The injection might feel the same. But if the peptide has been degraded, you may be injecting inactive protein solution, which carries the risk of getting no therapeutic benefit at all, which matters if weight management is a health priority for you right now.

Contact our support team, your prescriber, or the dispensing pharmacy straight away. Replacement may be possible depending on circumstances; at the very least you'll get a clear answer rather than a guess. The same applies if you're considering managing a side effect and wondering whether the pen's history is relevant, it sometimes is.

For background on how the wider semaglutide medicine range is structured in the UK, the semaglutide dosing guide walks through the escalation schedule, and our semaglutide side effects page covers what to watch for during treatment. If you'd like to understand how Wegovy compares across available dose strengths, the highest Wegovy dose page has the detail. You can also explore all available weight-loss treatment options if you're still at the research stage.

Semaglutide is a prescription-only medicine, a clinician assesses suitability before any treatment begins, and that clinical relationship is the right place to take storage questions too. If you'd like to start that conversation, you can begin a free consultation with one of our GPhC-registered prescribers today.